Without ever having tried it: inkscape can open svg and pdf and save to dxf, which can be imported in saga gis. Most likely you will loose most if not all of the formatting of the file, but if you are lucky you could perhaps recover some lines/polygons or points from the drawing.

You would have to georeference those anyway, so I would rather stick to a drawing program like inkscape to keep the information and export those things from gis which you would need.